The present invention relates to a device for the application of a system of opening and closing a packaging, denoted in the field by the name of xe2x80x9czipxe2x80x9d, which can be installed on a vertical packaging machine.
For the application of the zip, which requires feeding in a transverse direction in relation to the direction of feeding of the wrapping for packaging, the current most widespread techniques involve the use of grippers or devices for the creation of the vacuum, designed to grip the zip and to transport it into the correct welding position.
Welding of the zip to the wrapping is divided into a first phase upstream of the forming tube which only involves the male element of the zip and a successive phase downstream of the forming tube wherein the female element of the zip is welded to the wrapping.
Traditional devices for the application of the zip are found however to be slow and inaccurate.
The speed of application of the system of opening and closing onto the wrapping for packaging is an important factor in determining the productivity of the plant and hence the cost of the finished product.
The precision in determining the point of the wrapping whereto the system of opening and closing is to be applied also avoids considerable waste of material. In a process of mass-packaging even small errors of positioning of the zip on one packaging and on the successive one can combine and become no longer negligible, creating packaging with a length substantially different from that set and which therefore should be eliminated.
For correct welding of the zip it is also necessary for the zip band to be welded to be perfectly aligned with the welding plate both in the first and in the successive phase of welding. Thus to avoid having to define at welding the relative position between welding machine and zip within extremely narrow tolerances, there is a tendency nowadays to use a zip with oversized width, so as to create always an area of overlap between zip and welding machine. Naturally this causes a further waste of materials, specifically materials used for manufacturing the zip.
The main object of the present invention is in fact that of overcoming the disadvantages suffered in the known art, and in particular of providing on a vertical packaging machine a device for the application of a highly productive and precise system of opening and closing the packaging, so as to limit or eliminate completely any possible waste of materials.
Another object of the present invention is that of providing a device for the application of a simple and inexpensive system of opening and closing. Yet another object of the present invention is that of providing a perfected method for application of the zip to the wrapping.
These objects of the present invention are achieved by a device in accordance with the independent claim included hereinbelow.
The invention provides an assembly of a vertical packaging machine and a device for the application of a system of opening and closing the packaging or zip formed by two superimposed elements which can be removably engaged, wherein the vertical packaging machine comprises a framework supporting in succession a feeder of the wrapping for packaging, a vertical forming tube and a welding unit for welding the transverse edges of the formed wrapping, and wherein the device for application of the system of opening and closing, handled by a programmable controller, comprises: upstream of the forming tube, a carriage slidingly supported by the framework of the machine in the direction of forward movement of the wrapping to be formed; a first welding unit supported by said carriage for a first phase of welding of the zip; means supported by said carriage for positioning the zip on the wrapping in the position of the first weld of the zip; and, downstream of the forming tube and of the first welding unit, a second welding unit for a final phase of welding of the zip to the packaging.
In accordance with a preferred method of application of the zip, the front edge of the male element of the zip is welded to the wrapping by the first welding unit, while the remaining edges of the zip are only welded subsequently by the second welding unit.
Advantageously the carriage handled by the programmable controller can slide in relation to the wrapping so as to seek on the wrapping the set position of welding of the zip and accurately position the first welding unit there. In order to increase the production rate it is possible to place the carriage on the framework of the machine in a reference position close to the welding position provided, in such a way that seeking the position of welding on the wrapping only requires a short stroke and hence a brief time of movement for the carriage.
Advantageously means are also introduced for aligning the zip with the welding plate of the second welding unit and proceeding with its correct final welding.